Subminiature variable capacitor



Nov. 17, 1964 w. H. KUMM ETAL 3,157,834

SUBMINIATURE VARIABLE CAPACITOR Filed July 6, 1961 INVENTORS WILLIAM H. KUMM BY WILLIAM L. ETSCH W Y/ATTOR AGENT United States Patent w. Y i o up i liiAiUsall.

Kumrn a .t

This invention relates to a subrniniature variable capacr tor for use in high it" equency tuned circuits.

One object of the invention is to provide a variable capacity element capable of obtaining a minimum capacity Of 0.1 ,LL/Lf.

Another object of the invention is to provide a subminiature variable capacitor which is substantially temperature and mechanically stable.

A further object of the invention is to provide a subminiature variable capacitor element capable of being mounted on a chassis so that the capacitance between the terminals of the capacitor element and the chassis does not exceed the capacitance between the electrodes of the capacitor by a great amount.

These and other objects will be more fully understood from the following detailed description taken with the drawing, wherein:

FIG. 1 shows an exploded perspective view of the variable capacitor of the invention;

PlG. 2 shows a side View of the assembled device of PEG. 1 mounted on a panel; and,

FIG. 3 shows a sectional view of the device of FIG. 2 along the line 33.

The principal use for a physically small, low capacity variable capacitor is in the neutralization of the interelectrode capacity of vacuum tubes in high frequency tuned amplifiers. The order of capacity necessary for this purpose is from 0.1 out. to about 1.5 out. depending on the circuit. There are some relatively small commercially available capacitors having a minimum capacity of 0.5 b, however, this is too much for some or" the circuits aside from the fact that these capacitors have to be mounted mechanically which requires considerable space in order that the capacity from either of the terminals to the chassis ground of the tuned amplifier shall not be many times greater than that between each of the terminals of the unit.

Referring more particularly to PEG. 1 of the drawing, reference number in refers to a dielectric stand-oil member made of a material such as polytetralluoroethylene, known in the art as Teflon having a projection 11 thereon for mounting the capacitive element on the chassis indicated generally at 13 in the manner shown in F168. 2 and 3. The diameter of the projection 11 on member 19 should be slightly larger than the opening 12 in chassis 13 so that the cold flow properties of the Teflon may be used for securing the capacitor.

A brass plug 14 having a projection 15 with two square tapered securing projections 16 and 17 thereon is received and retained in a central bore hole 18 in the stand-oft member 16. The square projections 16 and 17 secure the plug to the stand-oil to prevent rotation of the brass plug 14 in the stand-off 113. The brass plug 14 has a threaded central bore hole 1) therein for receiving a T etlon spacer member 20. The outer diameter of the projection 21 on spacer member 2% is made slightly larger than the larger diameter of threaded bore hole 19 to provide a tight fit between members 20 and 14 when the spacer 20 is threaded into the bore 19. A hexagonal head 22 is provided on member 2b which is used to vary the capacity.

A central bore hole 23 is provided in the spacer member for receiving a steel pin 24. The outer diameter of 24 is slightly larger than bore hole 23 to provide a tight fit. A shoulder 25 on steel pin is for retaining the pin in member 24 Pin is free to rotate in member 29 because of the lubricating property of Teflon so that the circuit lead wire (not shown) when connected to pin 24 does not have to accommodate rotation, The other lead (not shown) is connected to brass plug 14.

the operation of the variable capacity element of this invention, pin 24 is moved with respect to brass plug 14 by turning the spacer member 26!) in the screw threads in member 14.

As described above, due to the lubricating properties of Teflon there is substantially no rotation of the pin as the capacity is changed. The tight fit of the various elements makes the capacitor sturdier and less subject to capacity chan c with temperature changes and vibration. Use is made of the cold flow properties of Teflon in making the tight fits. While threads are shown on projection 21 these need not be precut but rather the Teflon spacer may be permitted to thread itself as it is turned into the threaded bore 19.

While this device has been described with an insulator stand-oil type of support, the bore hole can be provided through the projection 11 on element it? to provide a feed through type insulator support.

There is thus provided a subminiature variable capacitor for use in high frequency tuned circuits.

While certain specific embodiments have been described in detail, it is obvious that numerous modifications may be made without departing from the general principle and scope of the invention.

We claim:

A subminiature variable capacitive device comprising: an elongated metal body having a bore hole centrally located and threaded along a substantial length of the longitudinal axis of said metal body, a polytetrafiuoroethylene spacer member retained within said centrally located and threaded bore hole, said spacer member having a cylindrical bore hole, a metal pin having a circular cross-section snugly fitted Within said cylindrical bore hole of said spacer member, a raised shoulder on said metal pin for securing said pin in said spacer, means on said spacer for rotating the spacer within said centrally located and threaded bore hole for adjusting the axial position of said metal pin with respect to said elongated metal body, a second polytetratluoroethylene support having a central bore hole therein, means on said elongated metal body for engaging said bore hole within said second polytetrafiuoroethylene support for securing said elongated metal body to said second polytetrafiuoroethylene support and a mounting projection on said support at the end remote from said metal body.

References Cited by the Examiner UNITED STATES PATENTS 1,632,130 6/27 Haddock 317249 2,677,794 5/54 Gutterman 317-249 2,774,017 12/56 Shapp et al. 317249 FOREIGN PATENTS 212,199 3/24 Great Britain.

E. JAMES SAX, Primary Examiner.

JOHN F. BURNS, Examiner. 

